Lecture: Growth and Development, Part 3B

Biology of Fungi

Fungal Growth and Development

BIOL 319

Sexual Development (cont.)

  Nature of sexuality   Homothallic vs. heterothallic

  Governed by mating type genes

(compatibility)   Arrangement of mating types   Bipolar compatibility - governed by a single gene

locus where one of a non-allelic pair of genes

(idiomorph) exists   Tetrapolar compatibility - two mating type gene pairs

of multiple idiomorphs

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BIOL 319 - Spring 2017

Sexual Development

  Sexual reproduction involves three

fundamental processes:   Plasmogamy - fusion of haploid cells

  Karyogamy - fusion of haploid nuclei  

Meiosis - reduction division   Two fundamental points of sexual

reproduction   Nature of sexuality   Serves as a survival mechanism

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Sexual Development (cont.)   Mating type and

hormonal control

  Chytridiomycota

  Allomyces is a

homothallic fungus

that produces

separate male and

female gametangia

that release motile Gametangia of Allomyces. Source: www.palaeos.com/

gametes

Fungi/Lists/Glossary/GlossaryG.html

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Sexual Development (cont.)

BIOL 319

Sexual Development (cont.)

  Mating type and hormonal control   Chytridiomycota (cont.)

  Females release a pheromone, serinin, that attracts

the male gametes   Male gametes move along a concentration gradient

  Serinin and carotenoid color produced in male

gametangia are produced from the same precursor,

indicating mating type gene controls development of

the sex organs

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Lecture: Growth and Development, Part 3B

Sexual Development (cont.)

  Oomycota   Homothallic or heterothallic, but in

most cases produces a colony

with both male and female sex

organs (antheridia and oogonia)   Mating type genes control

compatibility   Hormonal control in Achlya

  Female produces antheridiol

causing the male to increase

production of cellulase which

induces hyphal branching to

increase

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BIOL 319 - Spring 2017

Sexual Development (cont.)

  Once triggered by

antheridiol, males release

oogoniols that induce

oogonia development   Eventually, male branches

(antherida) fuse with

oogonia

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Sexual Development (cont.)

Oogonium and antheridium of Achlya. Source:

www.palaeos.com/Fungi/Lists/Glossary/GlossaryG.html BIOL 319

Trisporic acid hormonal system in mating within the Zygomycota.

Sources: www.palaeos.com/Fungi/Lists/Glossary/GlossaryG.html

and Deacon, 2006 BIOL 319

Sexual Development (cont.)

  Zygomycota   Homothallic or heterothallic

  Two mating type genes that govern conversion of β-

carotene to a prohormone   Prohormone is eventually converted by mating-type

specific gene to trisporic acid   Trisporic acid volatilizes and causes hyphae of

opposite mating type to grow towards one another

and fuse to form a zygospore BIOL 319

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Lecture: Growth and Development, Part 3B BIOL 319 - Spring 2017

Sexual Development (cont.)

  Ascomycota   Typically two mating types a cells and α cells   Best characterized system is that of Saccharomyces

  Mating is controlled by the MAT gene locus of

flanked by two other loci, MATa and MATα   A copy of one loci is made and inserted into MAT

gene locus - this is now the mating type of the cell   This copy can switch out after each new bud cell is

produced

Mating type loci of Saccharomyces. Source: nitro.biosci.arizona.edu/courses/ EEB320-2005/Lecture13/lecture13.html

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Diagram of life cycle of Saccharomyces. Source: nitro.biosci.arizona.edu/

courses/EEB320-2005/Lecture13/lecture13.html BIOL 319

Sexual Development (cont.)

  Ascomycota (cont.)   MATα are responsible for producing:

  Peptide hormones a-factor and α-factor  

Hormone receptors   Cell surface agglutinins

  α cells constitutively release α-factor that is

recognized by a receptor on a cells   a cells cease growth and arrest at G1 phase of the

cell cycle, then release a-factor

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Sexual Development (cont.)

  Ascomycota (cont.)   Different mating types then form outgrowths

(“schmoo” cells) with strain specific agglutinins on

their surfaces   Agglutinins cause cells to bind to one another, which

then leads to fusion (plasmogamy), followed by

karyogamy (diploid formation)   Subsequent induction of meiosis produces four

ascospores BIOL 319

“Schmoo cell”, formation of zygotes via fusion of yeast cells,

and ascospores of Schizosaccharomyces. Sources:

www.biomade.nl/AmphipathicProteins.htm, www.jbc.org, www.visualsunlimited.com/browse/vu227/vu227486.html and,

BIOL 319 3

Lecture: Growth and Development, Part 3B BIOL 319 - Spring 2017

Diagram of life cycle of Saccharomyces. Source: www.brooklyn.cuny.edu/bc/ahp/LAD/C9/C9_tetrads.html

Sexual Development (cont.)

  Basidiomycota   Most are heterothallic having one or two mating type

loci (typically termed A and B) with mulitiple idiomorphs

at each locus (e.g., A1, A2, A3, etc.)   Successful matings occur with different idiomorphs at

each locus (e.g., A1, B1 x A2, B2)   Different pairings of idiomorphs have allowed a

dissection of the functions of the mating-type genes   A locus - controls pairing and synchronous division

of nuclei and initiation of clamp formation   B locus - controls septal dissolution, fusion of

clamp branches, and increased glucanase

activity BIOL 319

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Mating reactions between haploid isolates of Armillaria ostoyae (with bifactorial mating system): 1.

Incompatible mating (incompatibility factors A1B1 x A1B1). 2. hemicompatible I (incomp. factors A1B1

x A1B2). 3. hemicompatible II (incomp. factors A1B1 x A2B1). 4. compatible mating, resulting in diploid

mycelium (incomp. factors A1B1 x A2B2).Source: www.padil.gov.au/viewPest.aspx?id=518 BIOL 319

Species identification with the aid of mating test. 1. A. ostoyae haploid (lower) x A. borealis

haploid (intersterile – no reaction). 2. A. ostoyae diploid (lower) x A. borealis haploid (intersterile –

no reaction). 3. A. ostoyae haploid x A. ostoyae haploid (compatible – rapid diploidisation). 4. A.

ostoyae diploid (lower) x A. ostoyae haploid (intersterile – slow diploidisation of the haploid

tester) .Source: www.padil.gov.au/viewPest.aspx?id=518 BIOL 319

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